Over half of Android devices are vulnerable to known security flaws that can be exploited by malicious applications to gain complete access to the operating system and the data stored on it, according to a report from mobile security firm Duo Security.

This conclusion is based on scans performed during the last couple of months with X-Ray, a free Android vulnerability assessment tool developed by Duo Security. X-Ray scans devices for known privilege escalation vulnerabilities that exist in various versions of the mobile operating system.

Privilege vulnerabilities can be exploited willingly by users in order to gain administrator (root) access on their devices and, for example, replace the firmware provided by the manufacturer with a custom-built one.

However, they can also be exploited by malware for malicious purposes and there have been multiple documented cases of Android malware that incorporated root exploits over the years.

"Since the launch of our mobile security solution, root exploits have been some of the most frequently encountered threats," Bogdan Botezatu, a senior e-threat analyst at antivirus vendor BitDefender, said Friday via email.

For example, during the first quarter of 2012, the top 10 detected Android threats included the "Rage Against The Cage" exploit, the "GingerBreak" exploit, the "Exploid" exploit and the "Asroot" exploit, Botezatu said.

Some of those cases might have been caused by users who were attempting to "root" their devices. However, others were likely generated by malicious apps that used those exploits, Botezatu said.

Over 50 percent is actually a fairly conservative estimate, Oberheide said. "Yes, it's a scary number, but it exemplifies how important expedient patching is to mobile security and how poorly the industry (carriers, device manufacturers, etc) has performed thus far."

The slow deployment of security patches to Android devices is a problem that has been known of for years. Manufacturers stop issuing updates for some device models too quickly and even when they do issue updates, some carriers don't distribute them in a timely manner.

"In the Microsoft ecosystem, desktop users know that patches are provided for quite a while, just like what happened with Windows XP," Botezatu said. "Mobile carriers, on the other side, see the mobile device, as well as the operating system running atop of it as a wearable item that rapidly goes out of fashion and has a shorter lifespan than desktops or laptops."

"While it's well-known in the security community that slow patching of vulnerabilities on mobile devices is a serious issue, we wanted to bring greater visibility to the problem," Oberheide said. The researcher will present the preliminary results from the X-Ray project at the United Security Summit conference in San Francisco on Friday.